With the adaptation of Roald Dahl's much-loved children's novel now running until 31 May 2014, an extra half a million tickets were, in a pre-planned move, placed on sale this morning. However, a set of mixed reviews – some effusive, some damning – published this morning mean the jury is out on whether they're golden or not.

However, initial gripes look unlikely to dent the commercial chances of a show that has already been seen by more than 70,000 people since previews started last month. Guests at last night's opening gala included Sarah Jessica Parker, Matthew Broderick and Uma Thurman – as well as members of Dahl's family.

David Greig's adaptation has also widened the show's international appeal, by changing the nationalities of the golden ticket winners to reflect a global audience.

Generally speaking, Mark Thompson's designs have shared the plaudits with Douglas Hodge's leading performance as Willy Wonka, while songs by Hairspray writers Marc Shaiman and Scott Wittman have carried the weight of criticism. Several reviews declare Pure Imagination – Leslie Bricusse and Anthony Newley's song from the 1971 film starring Gene Wilder – the musical's only memorable tune. Sam Marlowe writes that the original numbers "roll flavourlessly by until they merge into a single-click butterball of inconsequentiality". Variety's David Benedict believes "too many songs sound like exercises in style".

However, most critics have praised the show's sheer sense of spectacle. Billington applauds "a sumptuous visual feast", while the Telegraph's Charles Spencer writes: "The sets are massive, the special effects amazing."

Hodge, too, receives his share of praise for a performance that Spencer calls "splendidly charismatic and disconcerting". Hodge has deviated from both Wilder's version and Johnny Depp's freakier version for Tim Burton's 2005 film. Instead, his Willy Wonka is "a wonderfully unstable cross between a visionary with a screw loose and a Prospero-like figure with a serious game plan and a yearning to retire", according to the Independent.

However, the general attitude towards the new musical is that it can't rival another Dahl musical, this one by the RSC. "Be fair," writes the Times critic Libby Purves, in words that are sure to rankle the creative team, "it can't help not being Matilda."